Green Roof Membranes - A Buying Guide

Membranes are an essential component of a green roof, and there are many different types available - each suited to a particular green roof system.

We break down each of our green roof membranes, exploring the pros and distinctions of each product so you can find the right one for your project.

• Jump to green roof membrane comparison table

What are green roof membranes?

Green roof membranes are typically HDPE or composite drainage sheets that sit between the primary waterproofing layer on the structure (sometimes the root barrier when specified), and the substrate layer of a green roof. Their function is to:

• Protect the primary waterproofing layer
• Manage water within the roof system
  • Some membranes solely allow excess water to drain away
  • Some membranes both store water to support vegetation during dry periods, and drain water away
• Provide additional load distribution for pedestrian or vehicle use where required

Types of green roof membranes

Different green roof membranes are made for different types of green roofs. A membrane for an intensive green roof that supports vehicle traffic will be very different from those designed for an extensive green roof.

Our PRO membranes

Demand for durable, sustainably manufactured drainage membranes continues to grow. Our PRO range has been developed to deliver reliable, fast drainage while incorporating recycled HDPE across much of the range. The result is a balance of structural strength, water management performance, and a 30-year guarantee against deterioration. Our range covers the requirements of almost any type of green roof.

PermaSEAL PRO 20P

The PermaSEAL PRO 20P acts as a drainage layer and a large-volume water storage membrane, featuring 20mm cavities. Suited to both low-pitch and flat green roofs as well as intensive, semi-intensive and extensive systems.

• Application: Supplied in 20m² rolls, it’s easy to handle and install
• Use for: Extensive sedum, wildflower and biodiverse systems. Also suitable for inverted roofs.
• Storage/drainage capacity: Water storage capacity of approximately 6 l/m². Water drainage capacity of approximately 9 l/s/m
• Benefits:
  • Guaranteed against deterioration for 30 years
  • Manageable roll size and weight for one person
  • 20mm cavities for a high water retention capacity
  • High compressive strength (150kN/m²) and is tough and durable
• Coverage: Each roll is 2m x 10m (20m²)
• Stud height: 20mm
• Composition: Recycled HDPE

PermaSEAL PRO 25P

The PermaSEAL PRO 25P works as both a green roof drainage layer and large volume water storage membrane, featuring 25mm cavities. It’s designed for intensive and extensive green roof systems and is available in roll and board versions.

• Application: Rolls of 25P incorporate a bonded geotextile layer with a 25mm cavity that prevents slip and compression and is protected against soil obstruction. This saves time on installation compared with loose-laid geotextile. It can be laid over a suitable primary waterproofing layer (a root barrier may be required in some systems).

25P slabs are supplied without a bonded geotextile. They are ideal for smaller DIY projects thanks to their more manageable size and weight.

• Use for: Extensive lightweight sedum or wildflower blanket system, biodiverse/brown roofs and seed mixes. Also suitable for inverted roofs.
• Storage/drainage capacity: Water storage capacity of approximately 11 l/m². Drainage capacity of approximately 9.8 l/s/m
• Benefits:
  • Has a high compressive strength of 150 kN/m²
  • Features a fully-bonded geotextile filter fabric that speeds up installation
  • Has an all-in-one drainage, storage and filter layer
• Coverage: Supplied either as a 1m x 10m (10m²) roll, 2m x 10m (20m²) roll or 1m x 2m (2m²) board
• Stud height: 25mm
• Composition: Recycled HDPE

PermaSEAL PRO 40P

The PermaSEAL PRO 40P is designed for intensive green roof systems and commercial and residential projects. It functions as a drainage layer and a large water volume storage membrane, with 40mm cavities. It’s supplied as 2m² sheets.

• Application: Supplied as individual 1m x 2m (2m²) slabs. After applying the primary waterproofing layer and root barrier/slip, lay the slabs horizontally across the length of the roof with the cavity openings facing up.
• Use for: Biodiverse/brown roofs, seed mixes, intensive turf lawns, intensive trees and shrubs, paving and artificial grass
• Storage/drainage capacity: Water storage capacity of approximately 15 l/m². Drainage capacity of approximately 4.30 l/s/m (at hydraulic gradient i = 1.00)
• Benefits:
  • Guaranteed against deterioration for 30 years with a life expectancy equal to the design life of the structure
  • Pressure resistance of approx. 200 kN/m² and compressive strength of approx. 20 tonnes per m²
• Coverage: Each slab is 1m x 2m (2m²)
• Stud height: 40mm
• Composition: Recycled HDPE

PermaSEAL PRO 60P

The PermaSEAL PRO 60P delivers huge drainage and water storage capacity for intensive green roofs and commercial/residential projects. It has 60mm perforated cavities with a water storage capacity of around 20 l/m². The membrane is supplied in 1m x 2m sheets.

• Application: Supplied as individual 1m x 2m (2m²) slabs. After applying the primary waterproofing layer and root barrier/slip, lay the slabs horizontally across the length of the roof with the cavity openings facing up
• Use for: Intensive turf lawns, intensive trees and shrubs, paving and artificial grass.
• Storage/drainage capacity: Water storage capacity of approximately 20 l/m². Drainage capacity of approximately 4.48 l/s/m (at hydraulic gradient i = 1.00)
• Benefits:
  • High water storage capacity and stormwater attenuation
  • Easy to install with slabs manageable by one person
  • Guaranteed against deterioration for 30 years with a life expectancy equal to the design life of the structure
  • Pressure resistance of approximately 200 kN/m² and compressive strength of approximately 20 tonnes per m²
• Coverage: Each slab covers 1m x 2m (2m²)
• Stud height: 60mm
• Composition: Recycled HDPE

PermaSEAL PRO 8

The PermaSEAL PRO 8 is suited to low-pitch and flat intensive and extensive systems, as well as walkable and drivable deck paving drainage uses. Featuring 8mm studs with a drainage capacity of approximately 2.24 l/s/m. Available in 2m x 10m and 2m x 20m rolls.

• Application: After applying a primary waterproofing layer to the concrete roof deck or screed (and a root barrier or slip layer if required), roll out the membrane across the length of the roof. You can overlap the ends of two rolls, connecting the cavities. Then, where necessary, cut the membrane to size.
• Use for: Extensive lightweight sedum system and walkable and drivable paving
• Drainage capacity: Drainage capacity of approximately 2.24 l/s/m
• Benefits:
  • Fully bonded geotextile prevents slip and compression, and siltation of the studs
  • Tough and durable, with a compressive strength of 250kN/m²
• Coverage: Each roll covers 2m x 10m (20m²) or 2m x 20m (40m²)
• Stud height: Approximately 8mm
• Composition: Virgin HDPE

PermaSEAL PRO 11 Geodrain

Our PRO 11 Geodrain is a two-core drainage membrane that consists of a high-quality geotextile layer bonded to an HDPE drainage membrane. Thanks to its design, it remains effective even under heavy loading and traffic, making it the ideal solution for fast surface drainage for podium decks, buried roofs, terraces and balconies.

• Application: Application is different for horizontal and vertical installation. Refer to our datasheet for full guidance and instructions
• Use for: Podium decks, buried roofs, balconies and terraces, and flat extensive and intensive green roofs
• Drainage capacity: Drainage capacity of up to 3.15 l/s/m
• Benefits:
  • Unique reinforced and grooved stud design that securely interlocks a row of studs on overlapping membranes
  • Protects the primary waterproofing layer against mechanical damage
  • Promotes rapid water drainage to help reduce the risk of waterlogging and freeze-thaw stress
  • High compressive strength of 500kN/m²
  • Impact sound reduction for insulated flat roof structures of up to 34 dB - approved to BS EN ISO 10140
• Coverage: Each roll covers 2m x 15m (30m²)
• Stud height: 11mm
• Composition: Virgin HDPE

The extras

Include:

• Filter layer - a geotextile filter layer that prevents soil and debris from clogging your green roof system.
• Root barrier - protect your primary waterproofing layer from root growth with this impenetrable root barrier.
• Fleece membrane - protects your waterproofing layer from mechanical damage, and can also act as a separation layer.
• MP 2C - our ultimate all-rounder: the MP 2C can be used as the waterproofing layer, if one doesn’t already exist on your roof deck.

Key considerations

All of our membranes are made to provide long-lasting, reliable performance, but which one you need depends on your project. The table below breaks down the key features and applications for each membrane so you can see which is right for your project at a glance.

Learn more

Content links:

• Download our PRO Green Roof Brochure
• The State of Green Roofs: Past, Present and Future

Why choose Permagard?

Permagard are trusted by professional installers and specifiers to deliver high-quality, long-lasting membranes that offer great value for money. We don’t just deliver the membrane - we can also help you with technical information and support to ensure your green roof project is a success. Browse our professional membrane range, or get in touch today.